Osseointegrated implants may be used to anchor prosthetic structures, bone substitutes, or corrective elements on the human skeleton. For example, dental and orthopedic Osseointegrated implants in the form of screws may be anchored to the jawbone via the mouth to support prosthetic substitutes for one or more missing, lost, removed, or damaged teeth. As another example, screw implants may be installed on the spinal column for the fixation of bars to support and space vertebrae.
Bones are generally made of a rigid outer layer and a vascularized spongy core. The thickness of each of these rigid and spongy regions is particular to the biology of each person. During installation of an implant, however, it is expected that part of the implant will remain in the rigid region and part in the spongy region. To increase the stability of the implant after installation, and to reduce the patient's healing time, both the amount of bone removed and the damage to the blood vessels in proximity to the implant should be minimized during installation.
Most implants available on the market are formed of a cylindrical, generally screw-shaped body adapted for insertion into the bone. The cylinder is usually made from a biocompatible metal, such as titanium and alloys thereof, and may be coated with other types of biocompatible materials, such as hydroxyapatite, and/or receive a surface treatment in order to improve the osseointegration quality of the surface.
The different implants often diverge in the characteristics and geometry of their threads, as persons in the art seek to improve the quality of implant engagement with the bone structure.
U.S. Pat. No. 8,029,285 to Holman describes an implant generally in the form of a threaded cylinder having a prosthetic interface at its upper end, also known as the coronal end. At the lower end of the implant, also known as the apical end, there is a cut that runs through multiple threads, forming a self-tapping structure. Upon inserting implants with this type of structure, the lower part tends to accumulate bone material, which makes it difficult for the cut material to exit, leading to a loss of the self-tapping effect. The same implant further includes a slight increase in the diameter of the cylindrical body in the coronal region. Such increase is intended to compress the rigid region of the bone at the final moment when installing the implant, with the intention of increasing stability after installation. There are significant drawbacks to use of the implant designs in Holman such as the accumulation of material and fluids in the bone cavity during the installation of the implant that can lead to osseointegration issues, resulting in extended healing time.
There have been attempts to reduce such accumulation of material and fluids in bone during installation. For example, EP 0 895 757 B1 to Corigliani describes providing drainage channels along with a body whose core to gradually compress the bone without retaining fluids.
U.S. Pat. No. 8,714,977 to Fromovich describes a dental implant that facilitates insertion including a body having a coronal end and an apical end opposite the coronal end. An implant-prosthetic interface region is provided adjacent the coronal end. A tapered region is adjacent the apical end. A variable profile helical thread extends along the tapered region. The thread becomes broader in the apical-coronal direction and higher in the coronal-apical direction. The threads include an apical side, a coronal side and a lateral edge connecting them. The variable profile thread includes an expanding length of the lateral edge while the distance of the lateral edge from the base is reduced in the direction of the coronal end. The implant also has a gradual compressing tapered core, a self-drilling apical end with a spiral tap, and a coronal end with and inverse tapering.
The use of a conical core permits insertion of the implant into a bore of smaller diameter, which will be widened during the insertion, preserving a larger amount of bone around the implant. The conical core further has the advantage of compressing the bone during installation, increasing the stability after insertion thereof. However, the use of wide threads makes it difficult to align the implant in the bore at the initial moment of insertion, which may call for adjustment during insertion leading to the undesirable result of increased bone loss. Excessively wide threads from conventional designs also may cause problems when the space for insertion of the implant is limited by the roots of adjacent teeth—especially in the molar region, where roots extend sideways, and cutting the root of a healthy tooth with the implant thread would damage, and may even lead to the loss of, the tooth. Furthermore, a wide thread cuts a larger amount of the vascularization around the implant region, which delays healing.
Additionally, the continuously cut self-tapping structure concentrated in the apical portion of conventional implants suffers from drawbacks of accumulation of material within the self-tapping structure, increasing risks of osseointegration issues leading to extended healing time.